1. Field of the Invention:
The present invention relates to a process for forming a pattern of metallurgy on the top of a ceramic substrate.
2. Description of the Prior Art:
A relatively recent innovation in electronic packaging has been the development of the multilayer ceramic (hereafter MLC) module. In this technology "green" sheets of ceramic powder held together by a temporary organic binder are metallized with a noble or refractory metal, usually, but not mandatorily, by screen printing. The metallized sheets are stacked, laminated and fired to form a monolithic ceramic-metal package. Details on MLC technology are given in SOLID STATE TECHNOLOGY, May 1972, Vol. 15, No. 5, pages 35-40, Kaiser et al, hereby incorporated by reference.
It is known that "green" sheets as described shrink non-uniformly during sintering, and that this non-uniform shrinkage can cause filled via holes within the ceramic substrate to be out of alignment with a top layer of metallurgy which is deposited after sintering.
IBM Technical Disclosure Bulletin, Vol. 22, No. 12, May, 1980, pages 5328 and 5329 discloses that the via holes (hereafter often merely vias) in MLC structures are often misregistered after sintering due to non-uniform shrinkage of the ceramic. This Technical Disclosure Bulletin suggests using E-beam scans to record the location of vias on the top of the MLC, metallizing, applying a photoresist, E-beam exposing so that a 0.001 clearance is generated and then etching, leaving a rectangular pad with a clearance around the MLC via and the true location.
U.S. Pat. No. 3,905,818 Margrain discloses a method and an apparatus for printed circuit manufacture wherein an electrical circuit is traced on a metal layer or foil by one or several actinic light spots which are moved with respect to a photo-sensitive film with which the metal foil or layer is coated. An optical fiber strand is used which is moved relative to the photo-sensitive layer.
U.S. Pat. No. 3,651,567 Fenner et al discloses a method of making electronic components wherein an electrically conductive film is deposited on a substrate surface by a dry printing process which may comprise using a thin foil coated on one side with the material to form the electrically conductive film. The foil can be pressed against the substrate with a suitably shaped die causing the transfer of film-forming material from the foil to the substrate. The die is typically heated for the purposes of transfer.
U.S. Pat. No. 3,948,706 Schmeckenbecher discloses a method for forming metallized interconnection patterns on a ceramic green sheet with improved line definition and a process for metallizing via holes and recessed grooves in a ceramic green sheet, the major object of this patent being to avoid the use of a mask material and the attendant necessity for chemical etching. According to this patent, a sheet of a material such as a thermoplastic sheet is applied to a ceramic green sheet, openings are formed in the thermoplastic sheet in a desired pattern, a conductive metal paste is applied to the thermoplastic sheet to fill the openings and thereby form a metallized composite structure, the metallized composite structure is laminated to at least one other similar composite structure and the resulting laminated structure is fired to volatilize the thermoplastic sheet and sinter the ceramic green sheet.
U.S. Pat. No. 3,990,142 Weglin discloses a method of making a circuit board where a sheet of conductive foil is stamped by a die of a predetermined pattern against a dielectric substrate to shear out a foil section which is then pressed against the substrate while applying heat through the die to bond the sections using a thermal curing adhesive to the substrate. The dies must exhibit a rather specific structure.
U.S. Pat. No. 4,237,606 Niwa et al discloses a method for manufacturing a multi-layer ceramic board where a conductor land is formed and baked on a first substrate. A second substrate on which a wiring pattern is formed is then electrically connected to the first substrate via the land. Any errors due to shrinkage at the time of sintering are compensated for by the conductor land.